CPU always at 100%

We have a Patriot 750mHz PC; SiS BKS630 V7.1g via Cyrixiii 750mHz processor in our office which is used only for basic office applications, Word and Excel etc. It should be easily adequate for this and indeed used to be. It was running Windows ME which for whatever reason couldnt easily be loaded with Norton Antivirus also it did not Network at all well. We noticed that the CPU and Memeory were always full and that the system was getting to be very slow so, suspecting that a virus had gotten in we elected to format the disk and install Windows 2000 Pro which went very well.

Problem is that now that everything is running, including the latest version of and Antivirus program that the CPU is apparantly constatantly running at or near to 100%.

This manifests itself as a problem when running Word as the screen often freezez and cannot keep up with the text entry. It looks as though the processor is always busy doing something else.

I have heard of virus's or worms that reside behind the FAT which cannot be cleaned out by a simple format instruction, could it be this that is taking up all the CPU attention. If so how do I detect it and how to get rid of it. Norton certainly doesn't see anything on the disk to worry about.

Failing this is there any possibility that the CPU has a hardware failure of some sort which allows it to run but only allows limited use. I have run an old version of DOS Chekit but this looks fine.

Otherwise any hint as to how I can isolate the cause of teh CPU being permanantly busy.

Yes, as Callandor said, bring up task manager and see what's taking up your resources. Click the CPU tab to sort by it, scroll to the bottom and see what's eating up your CPU. If it's something you want running, right click it and go down to Set Priority and set it to something lower. If it's something you don't want running, end it.